Radiance

Physical size
Surname	Radiance
Formula symbol	${\displaystyle I}$
Size and unit system unit dimension SI W · sr -1 M · L 2 · T −3

Radiation intensity or radiation intensity , also called radiation intensity (but the term is also used in a different meaning - see intensity (physics) ), is a term from radiometry . The radiant intensity is the portion of the radiant power that is emitted by a radiation source (e.g. light source ) in a given spatial direction into the solid angle element of any small size : ${\displaystyle I}$ ${\displaystyle \mathrm {d} \Phi }$ ${\displaystyle \Phi }$ ${\displaystyle \mathrm {d} \Omega }$

${\displaystyle I\mathrm {d} \Omega =\mathrm {d} \Phi }$

The power is measured in watts (W), the solid angle in steradians (sr); the SI unit of the radiation intensity is therefore W / sr.

If the energy is radiated isotropically , i.e. within the entire solid angle of equally in each direction, the radiation intensity in each direction is: ${\displaystyle 4\pi \,\mathrm {sr} }$

${\displaystyle I={\frac {\Phi }{4\pi \,\mathrm {sr} }}\,}$.

Photometric equivalent

The corresponding quantity in photometry is the light intensity . It results from the radiant intensity by them with the photometric radiation equivalent , which includes the sensitivity curve of the human eye, weighted . ${\displaystyle I_{\mathrm {v} }}$

Relationship with other radiometric quantities

radiometric quantity	Symbol a)	SI unit	description	photometric equivalent b)	symbol	SI unit
Radiant flux radiant power, radiant flux, radiant power	${\displaystyle \Phi _{\mathrm {e} }}$	W ( watt )	Radiant energy through time	Luminous flux luminous flux, luminous power	${\displaystyle \Phi _{\mathrm {v} }}$	lm ( lumens )
Radiant intensity irradiance, radiant intensity	${\displaystyle I_{\mathrm {e} }}$	W / sr	Radiation flux through solid angles	Luminous intensity luminous intensity	${\displaystyle I_{\mathrm {v} }}$	cd = lm / sr ( candela )
Irradiance irradiance	${\displaystyle E_{\mathrm {e} }}$	W / m 2	Radiation flux through the receiver surface	Illuminance illuminance	${\displaystyle E_{\mathrm {v} }}$	lx = lm / m 2 ( lux )
Specific radiation emission current density, radiant exitance	${\displaystyle M_{\mathrm {e} }}$	W / m 2	Radiation flux through the transmitter surface	Specific light emission luminous exitance	${\displaystyle M_{\mathrm {v} }}$	lm / m 2
Radiance radiance, radiance, radiance	${\displaystyle L_{\mathrm {e} }}$	W / m 2 sr	Radiant intensity through effective transmitter area	Luminance luminance	${\displaystyle L_{\mathrm {v} }}$	cd / m 2
Radiant energy amount of radiation, radiant energy	${\displaystyle Q_{\mathrm {e} }}$	J ( joules )	by radiation transmitted energy	Amount of light luminous energy, quantity of light	${\displaystyle Q_{\mathrm {v} }}$	lm · s
Irradiation irradiation, radiant exposure	${\displaystyle H_{\mathrm {e} }}$	J / m 2	Radiant energy through the receiver surface	Exposure luminous exposure	${\displaystyle H_{\mathrm {v} }}$	lx s
Radiation yield radiant efficiency	${\displaystyle \eta _{\mathrm {e} }}$	1	Radiation flux through absorbed (mostly electrical) power	Luminous efficiency (overall) luminous efficacy	${\displaystyle \eta _{\mathrm {v} }}$	lm / W

^a)The index "e" is used to distinguish it from the photometric quantities. It can be omitted.

^b)The photometric quantities are the radiometric quantities, weighted with the photometric radiation equivalent K , which indicates the sensitivity of the human eye.

Individual evidence

1. ↑ Ludwig Bergmann , Clemens Schaefer : Optics: Wave and particle optics . In: Bergmann-Schaefer textbook on experimental physics . tape 3 . Walter de Gruyter, 2004, ISBN 3-11-017081-7 , p. 637 ( limited preview in Google Book search).
2. ↑ electropedia , International Electrotechnical Dictionary (IEV) of the International Electrotechnical Commission : Entries 731-01-23 (area "fiber optic communication") and 845-01-30 (area lighting) have the translation: radiant intensity = "radiation intensity"
3. ↑ Robert Wichard Pohl : Introduction to Optics . 8th edition. Springer, Heidelberg 1948, ISBN 978-3-662-01855-2 , p.  321 ff . (Online: [1] )
4. ↑ electropedia , International Electrotechnical Dictionary (IEV) of the International Electrotechnical Commission : Entry 705-02-04 (section "Communication by radio waves") has the translation radiation intensity = "Radiation intensity (in a given direction)"; the German edition of the dictionary , published by the German Commission for Electrical, Electronic and Information Technologies , adds the footnote: "In lighting technology, preferably referred to as radiation intensity".